(a) Field of the Invention
The present invention relates to a secondary battery, and more particularly, to a collector plate for a secondary battery which improves the welding efficiency during the manufacturing process of the battery.
(b) Description of the Related Art
Depending on the use or the power capacity of a battery, secondary batteries may be classified into lower power batteries (hereinafter “small battery”) in which one battery cell is made into a battery pack, and bulk size batteries (hereinafter “large battery”) in which several to tens of the secondary battery cells are connected to form a pack.
Small batteries are used as a power source for various portable electronic devices such as cellular phones, laptop computers, and camcorders. Large batteries are suitable for motor driven devices such as the electric vehicles.
Generally, small batteries have square and cylindrical shapes when they are made of one cell. A small battery includes an electrode assembly (jellyroll) in which a positive plate, a negative plate, and a separator as an insulator interposed between the positive and negatives plates are spirally-wound. The electrode assembly is inserted inside a cylindrical container to form the battery.
Lead terminals, that is, conductive tabs which collect the current produced from the positive and negative electrodes, are attached to the positive and negative plates. The conductive tab is fixed to the electrode assembly by welding to induce the current from the positive and negative electrodes to the positive and negative terminals.
When the above structure of a small battery is applied to a large battery, the dynamic kinetics necessary for large batteries may not be satisfied in terms of capacity and power. Accordingly, secondary batteries have been provided which include the multi-tab structure disclosed in, for example, Japanese Patent Publication No. 2003-7346, in which multiple tabs are attached to the electrode assembly. This secondary battery has a plurality of tabs formed along one direction of the electrode, and the tabs are fixed to an internal terminal which is connected with an external terminal.
The tabs of the secondary battery with the above structure may be integrally formed with a collector plate, or separately formed and welded to a collector plate.
However, when the tabs are integrally formed with the collector plate, material for the collector plate is wasted and the battery may not be able to satisfy the power characteristics required for the large battery. Additionally, when the tabs are separately formed, a large workforce is needed.
When the tabs are welded, heat generated from the tabs influences the electrode assembly. To minimize this influence, the tabs may have a relatively long length. However, long tabs occupy more space inside the battery, which in turn decreases the energy density per volume.
Additionally, a pack unit of the large battery used for hybrid electric vehicles requires high power dynamic kinetics due to its use characteristics. Accordingly, it is necessary that the tabs be designed to minimize the resistance element generated during the current collection process. However, since the above mentioned battery collects current through the tab with a small unit area, there is a problem that the resistance increases, which thereby decreases the collecting efficiency.